Methods for making a supported graft

ABSTRACT

A method for forming a self-expanding stent-graft, including coupling a shape memory member to a polymer cladding to form a polymer clad member, winding a length of the polymer clad member about a mandrel so that adjacent windings include regions of polymer cladding that overlap, heating the wound polymer clad member to join and seal the overlapping regions to one another, manipulating the stent-graft from a first diameter to a second diameter smaller than the first diameter, and loading the stent-graft into a restraining sheath, wherein the restraining sheath prevents the stent-graft from reverting to the first diameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/429,849, filed May 8, 2006, now U.S. Pat. No. 7,578,899, which is acontinuation of U.S. patent application Ser. No. 10/431,685, filed May8, 2003, now U.S. Pat. No. 7,060,150, which is a divisional of U.S.patent application Ser. No. 09/855,918, filed May 15, 2001, nowabandoned, which is a divisional of U.S. patent application Ser. No.08/999,583, filed Dec. 22, 1997, now U.S. Pat. No. 6,264,684, which is acontinuation-in-part of three applications: 1) International ApplicationNo. PCT/US95/16497, filed Dec. 8, 1995, which was nationalized as U.S.patent application Ser. No. 09/077,533, filed May 28, 1998, now U.S.Pat. No. 6,053,943; 2) U.S. patent application Ser. No. 08/833,797,filed Apr. 9, 1997, now U.S. Pat. No. 6,451,047, which is acontinuation-in-part of U.S. patent application Ser. No. 08/508,033,filed Jul. 27, 1995, now U.S. Pat. No. 5,749,880, which is acontinuation-in-part of U.S. patent application Ser. No. 08/401,871,filed Mar. 10, 1995, now U.S. Pat. No. 6,124,523; and 3) U.S. patentapplication Ser. No. 08/794,871, filed Feb. 5, 1997, now U.S. Pat. No.6,039,755. This application expressly incorporates by reference theentirety of each of the above-mentioned applications as if fully setforth herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to implantable intraluminaldevices, particularly intraluminal grafts. Intraluminal stents areimplanted in order to maintain luminal patency, typically afterinterventional methods have been employed to restore luminal patencyfrom a diseased state, exclude an aneurysmal condition, bypass anoccluded or obstructed anatomical region or to shunt body fluids.Surgically implantable prosthetics, particularly vascular prostheses,have been employed for many years. Expanded polytetrafluoroethylene(ePTFE) vascular grafts have been used as biocompatible implants formany years and the use of ePTFE as a bio-inert barrier material inintraluminal applications is well documented. Conventional ePTFEvascular grafts, however, typically lack sufficient diametric mechanicalrigidity to maintain luminal patency in intraluminal applications.

Conventional externally supported ePTFE vascular grafts, such as theIMPRA Flex-Graft or the Gore Ring Graft, have an external beading ofhelically wound non-expanded or solid polytetrafluoroethylene, or ofsolid fluorinated ethylene-propylene co-polymer (FEP). Non-expanded orsolid polytetrafluoroethylene is significantly more rigid than the ePTFEmaterial due to its higher density and absence of interstitial voids.These externally supported ePTFE vascular grafts are not well-suited tointerventional intraluminal procedures due to their inability to assumea reduced profile suitable for percutaneous delivery using a catheterand their inability to recover an enlarged diametric dimension in vivo.

Most intraluminal stents are formed of an open lattice fashioned eitherto be elastically deformable, such as in the case of self-expandingstainless steel spring stents, plastically deformable, such as in thecase of balloon-expandable stainless steel PALMAZ stents, or thermallyexpandable such as by employing shape memory properties of the materialused to form the stent. A common problem of most conventionalintraluminal stents is re-occlusion of the vessel after stent placement.Tissue ingrowth and neointimal hyperplasia significantly reduces theopen diameter of the treated lumen over time, requiring additionaltherapies.

The present invention makes advantageous use of the known biocompatibleand material properties of ePTFE vascular grafts, and adds an abluminalsupporting structure capable of being diametrically reduced to anintraluminal delivery profile and self-expanding in vivo to conform tothe anatomical topography at the site of intraluminal implantation. Moreparticularly, the present invention consists of an ePTFE substratematerial, such as that described in U.S. application Ser. No.08/794,871, filed Feb. 5, 1997, now U.S. Pat. No. 6,039,755, as acarrier for a helically wound, open cylindrical support structure madeof a shape memory alloy.

The inventive intraluminal stent-graft device may be implanted either bypercutaneous delivery using an appropriate delivery system, a cut-downprocedure in which a surgical incision is made and the intraluminaldevice implanted through the surgical incision, or by laparoscopic orendoscopic delivery.

Shape memory alloys are a group of metal alloys which are characterizedby an ability to return to a defined shape or size when subjected tocertain thermal or stress conditions. Shape memory alloys are generallycapable of being plastically deformed at a relatively low temperatureand, upon exposure to a relatively higher temperature, return to thedefined shape or size prior to the deformation. Shape memory alloys maybe further defined as one that yields a thermoelastic martensite. Ashape memory alloy which yields a thermoelastic martensite undergoes amartensitic transformation of a type that permits the alloy to bedeformed by a twinning mechanism below the martensitic transformationtemperature. The deformation is then reversed when the twinned structurereverts upon heating to the parent austenite phase. The austenite phaseoccurs when the material is at a low strain state and occurs at a giventemperature. The martensite phase may be either temperature inducedmartensite (TIM) or stress-induced martensite (SIM).

When a shape memory material is stressed at a temperature above thestart of martensite formation, denoted Ms, where the austenitic state isinitially stable, but below the maximum temperature at which martensiteformation can occur, denoted Md, the material first deforms elasticallyand when a critical stress is reached, it begins to transform by theformation of stress-induced martensite. Depending upon whether thetemperature is above or below the start of austenite formation, denotedAs, the behavior when the deforming stress is released differs. If thetemperature is below As, the stress-induced martensite is stable,however, if the temperature is above As, the martensite is unstable andtransforms back to austenite, with the sample returning to its originalshape. U.S. Pat. Nos. 5,597,378, 5,067,957 and 4,665,906 disclosedevices, including endoluminal stents, which are delivered in thestress-induced martensite phase of shape memory alloy and return totheir pre-programmed shape by removal of the stress and transformationfrom stress-induced martensite to austenite.

Shape memory characteristics may be imparted to a shape memory alloy byheating the metal at a temperature above which the transformation fromthe martensite phase to the austenite phase is complete, i.e., atemperature above which the austenite phase is stable. The shapeimparted to the metal during this heat treatment is the shape“remembered.” The heat treated metal is cooled to a temperature at whichthe martensite phase is stable, causing the austenite phase to transformto the martensite phase. The metal in the martensite phase is thenplastically deformed, e.g., to facilitate its delivery into a patient'sbody. Subsequent heating of the deformed martensite phase to atemperature above the martensite to austenite transformationtemperature, e.g., body temperature, causes the deformed martensitephase to transform to the austenite phase and during this phasetransformation the metal reverts back to its original shape.

The term “shape memory” is used in the art to describe the property ofan elastic material to recover a pre-programmed shape after deformationof a shape memory alloy in its martensitic phase and exposing the alloyto a temperature excursion through its austenite transformationtemperature, at which temperature the alloy begins to revert to theaustenite phase and recover its preprogrammed shape. The term“pseudoelasticity” is used to describe a property of shape memory alloyswhere the alloy is stressed at a temperature above the transformationtemperature of the alloy and stress-induced martensite is formed abovethe normal martensite formation temperature. Because it has been formedabove its normal temperature, stress-induced martensite revertsimmediately to undeformed austenite as soon as the stress is removedprovided the temperature remains above the transformation temperature.

The present invention employs a wire member made of either a shapememory alloy, preferably a nickel-titanium alloy known as NITINOL,spring stainless steel or other elastic metal or plastic alloys, orcomposite material, such as carbon fiber. It is preferable that the wiremember have either a generally circular, semi-circular, triangular orquadrilateral transverse cross-sectional profile. Where a shape memoryalloy material is employed, pre-programmed shape memory is imparted tothe wire member by helically winding the wire member about a cylindricalprogramming mandrel having an outer diametric dimension substantiallythe same, preferably within a tolerance of about +0 to −15%, as theePTFE substrate and annealing the programming mandrel and the wiremember at a temperature and for a time sufficient to impart the desiredshape memory to the wire member. After annealing, the wire member isremoved from the programming mandrel, straightened and helically woundabout the abluminal wall surface of an ePTFE tubular member at atemperature below the As of the shape memory alloy used to form the wiremember.

In order to facilitate bonding of the wire member to the ePTFE tubularmember, it is preferable that a bonding agent capable of bonding thesupport wire member to the ePTFE tubular member be used at the interfacebetween the wire member and the ePTFE tubular member. Suitablebiocompatible bonding agents may be selected from the group consistingof polytetrafluoroethylene, polyurethane, polyethylene, polypropylene,polyamides, polyimides, polyesters, polypropylenes, polyethylenes,polyfluoroethylenes, silicone fluorinated polyolefins, fluorinatedethylene/propylene copolymer, perfluoroalkoxy fluorocarbon,ethylene/tetrafluoroethylene copolymer, and polyvinylpyrolidone. Thebonding agent may constitute an interfacial layer intermediate the wiremember and the ePTFE tubular member, or may be a polymeric cladding atleast partially concentrically surrounding the wire member.

Where a cladding is provided, the cladding is preferably a polymericmaterial selected from the group consisting of polytetrafluoroethylene,polyurethane, polyethylene, polypropylene, polyamides, polyimides,polyesters, polypropylenes, polyethylenes, polyfluoroethylenes, siliconefluorinated polyolefins, fluorinated ethylene/propylene copolymer,perfluoroalkoxy fluorocarbon, ethylene/tetrafluoroethylene copolymer,and polyvinylpyrolidone. The cladding may be either co-extruded with thewire member, extruded as a tube into which the wire member isconcentrically inserted after annealing the wire member, or provided asan elongate member which a longitudinal recess which co-axially receivesthe wire member. Where the bonding agent employed is a meltthermoplastic which has a melt point below the crystalline melt point ofpolytetrafluoroethylene, the melt thermoplastic bonding agent and thewire member are wound about the ePTFE tubular member, and constrainedthereupon, such as by application of circumferential pressure, then theassembly is then exposed to the melt temperatures without longitudinallysupporting the assembly.

However, where the bonding agent is polytetrafluoroethylene, bonding ofthe wire member to the ePTFE tubular member requires exposing theassembly to temperatures above the crystalline melt point ofpolytetrafluoroethylene in order to effectuate bonding of the wiremember to the ePTFE. This is preferably accomplished by introducing theassembly into a sintering oven while the assembly is on a mandrel andthe assembly secured to the mandrel by an external helical wrapping ofTEFLON tape applied to opposing ends of the assembly to longitudinallyconstrain the assembly and reduce or eliminate the tendency of theassembly to longitudinally foreshorten during sintering.

BRIEF SUMMARY OF THE INVENTION

It is a primary objective of the present invention to provide aself-supporting, self-expanding stent-graft device which is capable ofbeing delivered to an anatomical position within a human body in a firstconstrained configuration, positioned in vivo at a desired anatomicalsite, and the constraint released to permit the stent-graft device totransform to a radially enlarged second configuration.

It is another primary objective of the present invention to provide astent-graft device which consists generally of tubular member fabricatedof a biocompatible polymer selected from the group of microporousexpanded polytetrafluoroethylene (“ePTFE”), polyethylene, polyethyleneterepthalate, polyurethane and collagen, and at least one winding of aelastically self-expanding wire coupled to either the abluminal orluminal surfaces of the ePTFE tubular member or interdisposed betweenconcentrically positioned ePTFE tubular members.

It is a further objective of the present invention to couple the atleast one winding of the elastically self-expanding wire to the ePTFEtubular member by cladding a support wire in a polymeric material whichhas a melt point less than or equal to that of the ePTFE tubular memberand below the A, temperature of the shape memory alloy metal wire.

It is a further objective of the present invention to provide anadhesive interlayer for bonding the shape memory alloy metal wire to thetubular member, the adhesive interlayer being selected from the groupconsisting of polytetrafluoroethylene, polyurethane, polyethylene,polypropylene, polyamides, polyimides, polyesters, polypropylenes,polyethylenes, polyfluoroethylenes, silicone, fluorinated polyolefins,fluorinated ethylene/propylene copolymer, perfluoroalkoxy fluorocarbon,ethylene/tetrafluoroethylene copolymer, and polyvinylpyrolidone.

It is another objective of the present invention to provide a method formaking a expanding stent-graft device comprised generally of an ePTFEtubular member and at least one winding of a shape memory alloy metalwire coupled to the abluminal surface of the ePTFE tubular member.

These and other objects, features and advantages of the presentinvention will be better understood by those of ordinary skill in theart from the following more detailed description of the presentinvention taken with reference to the accompanying drawings and itspreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a supported intraluminal graft inaccordance with a preferred embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1.

FIG. 4A is a side elevational cross-sectional view of a graft membermounted onto a mandrel in accordance with a preferred embodiment of themethod of the present invention.

FIG. 4B is a side elevational cross-sectional view of FIG. 4A with asupport member wrapped about an abluminal surface of the graft member.

FIG. 4C is a side elevational cross-sectional view as in FIGS. 4A and 4Billustrating an abluminal covering concentrically superimposed over theysupport member and the graft member.

FIG. 5 is a perspective view of a ribbon member clad in a polymericcovering in accordance with the present invention.

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 5.

FIG. 7 is a perspective view of a wire member clad in a polymericcovering in accordance with the present invention.

FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 7.

FIG. 9 is a diagrammatic cross-sectional view of a first embodiment of asupport member encapsulated in a shaped polymeric cladding covering.

FIG. 10 is a diagrammatic cross-sectional view of a second embodiment ofa support member encapsulated in a shaped polymeric cladding covering.

FIG. 11 is a diagrammatic cross-sectional view of a third embodiment ofa support member encapsulated in a shaped polymeric cladding covering.

FIG. 12 is a diagrammatic cross-sectional view of a fourth embodiment ofa support member coupled to a shaped polymeric cladding covering.

FIG. 13 is a perspective view of an alternative preferred embodiment ofthe supported intraluminal graft in accordance with the presentinvention.

FIG. 14 is a cross-sectional view taken along line 14-14 of FIG. 13.

FIG. 15 is a process flow diagram illustrating the process steps formaking the supported intraluminal graft in accordance with the method ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The shape memory alloy supported intraluminal graft 10 of the presentinvention consists generally of a tubular substrate 12 having a centrallumen 13 passing through an entire longitudinal extent of the tubularsubstrate. The tubular substrate 12 has a luminal wall surface 15adjacent the central lumen 13 and an abluminal wall surface 17 opposingthe central lumen 13. A support member 14 is provided and is preferablyat least partially covered by a polymeric cladding 11. The polymericclad support member 14 is circumferentially disposed about and joined tothe abluminal wall surface 17 of the tubular substrate 12, such as byhelically winding the polymeric clad support member 14 about theabluminal surface 17 of the tubular substrate 12. Optionally, a secondtubular substrate 19, having an inner diameter sufficiently dimensionedto be concentrically engaged about the abluminal wall surface 17 of thetubular substrate 12 and the polymeric clad support member 14, may beprovided.

In accordance with a first preferred embodiment of the presentinvention, and with particular reference to FIGS. 1-3, there is providedthe inventive supported intraluminal graft 10 comprised of a tubular 12made of a biocompatible polymeric material, such as expandedpolytetrafluoroethylene (“ePTFE”), polyethylene terepthalate (“PET”)such as that marketed and sold under the trademark DACRON, polyethylene,or polyurethane. Expanded PTFE substrate materials are preferably madeby ram extruding an admixture of polytetrafluoroethylene resin and ahydrocarbon lubricant to form a tubular extrudate, drying off thehydrocarbon lubricant, longitudinally expanding the dried tubularextrudate, then sintering the longitudinally expanded dried tubularextrudate at a temperature above the crystalline melt point ofpolytetrafluoroethylene.

The resulting tubular ePTFE material has a microporous microstructurewhich is composed of spaced-apart nodes interconnected by fibrils, withthe fibrils being oriented parallel to the longitudinal axis of theePTFE tube and parallel to the axis of longitudinal expansion. U.S. Pat.Nos. '390 and '566, both issued to Gore, teach processes for makingePTFE tubular substrates and are hereby incorporated by reference asteaching processes to make ePTFE tubular and planar materials. A tubularsubstrate may also be made by weaving yarn, made of either polyester orePTFE, into a tubular structure as is well known in the art.Additionally, the tubular substrate 12 may have a cylindrical profilehaving a substantially uniform internal diameter along its longitudinalaxis, or may have a tapered sidewall in which the tubular substrate 12assumes a generally frustoconical shape in which the internal diameterof the tubular substrate 12 increases or decreases along thelongitudinal axis of the tubular substrate 12. Alternatively, thetubular substrate 12 may have at least one region of stepped diameter inwhich the internal diameter of the tubular substrate changes at adiscrete longitudinal section of the tubular substrate 12.

In accordance with a first preferred embodiment of the presentinvention, the tubular substrate 12 is an extruded, longitudinallyexpanded and sintered ePTFE tubular member which has been radiallyexpanded from an initial luminal inner diameter of between about 1.5 mmto about 6 mm to a final luminal inner diameter of between about 3 mm toabout 18 mm. Thus, tubular substrate 12 is initially fabricated at afirst relatively smaller diametric dimension, dried of the hydrocarbonlubricant, and sintered, then radially expanded by application of anradially outwardly directed force applied to the luminal wall surface 15of the tubular substrate 12, which radially deforms the wall of thetubular substrate 12 from an initial luminal inner diameter, denoted D₁,to a second, enlarged luminal inner diameter, denoted D₂. Alternatively,tubular substrate 12 may be provided as an extruded, longitudinallyexpanded and sintered ePTFE tubular member having an inner diameterequivalent to the final inner diameter of the supported intraluminalgraft, e.g., extruded to a luminal diameter of between about 3 mm toabout 18 mm, and a wall thickness sufficient to acceptably minimize thedelivery profile of the supported intraluminal graft. Suitable wallthicknesses for the non-radially expanded ePTFE tubular member areconsidered less than or equal to about 0.3 mm for delivery to peripheralanatomic passageways.

The tubular substrate 12 is preferably radially expanded by loading thetubular substrate 12, in its fully or partially sintered state, onto aninflation balloon such that the tubular substrate 12 is concentricallyengaged upon the inflation balloon, introducing the inflation balloonand tubular substrate 12 into a tubular housing defining a generallycylindrical cavity having an inner diameter corresponding to the maximumdesired outer diameter of the final shape memory alloy supported graft,and applying a fluid pressure to the inflation balloon to inflate theinflation balloon and radially deform the tubular substrate 12 intointimate contact with the generally cylindrical cavity. Pressure ismaintained within the inflation balloon for a period of time sufficientto minimize the inherent recoil property of the ePTFE material in thetubular substrate 12, then the pressure is relieved and the inflationballoon permitted to deflate. The radially deformed tubular substrate,now having an inner luminal diameter D₂, is removed from the generallycylindrical cavity for subsequent processing.

During radial expansion of the tubular substrate 12 from D₁ to D₂, thenode and fibril microstructure of the ePTFE tubular substrate isdeformed. The nodes, which have an orientation perpendicular to thelongitudinal axis of the tubular substrate 12 and parallel to the radialaxis of the tubular substrate 12, deform along the longitudinal axis ofeach node to form elongated columnar structures, while the length of thefibrils interconnecting adjacent pairs of nodes in the longitudinal axisof the tubular substrate 12, remains substantially constant. The fibrillength is also referred to herein as the “internodal distance.”

A support member 14, which is preferably made of an elastic wirematerial selected from the group of thermoelastic or shape memoryalloys, spring stainless steel, elastic metal or plastic alloys, orcomposite materials, such as woven carbon fibers. Where a shape memoryalloy is employed, it is important that the shape memory alloy have atransition temperature below human body temperature, i.e., 37 degreesCelsius, to enable the shape memory alloy to undergo transformation tothe austenite phase when the shape memory alloy wire member is exposedto human body temperature in vivo. In accordance with the best modecurrently known for the present invention, the preferred shape memoryalloy is a near equiatomic alloy of nickel and titanium.

To facilitate attachment of the elastic or thermoelastic wire member 14to the tubular substrate 12, it is contemplated that a polymericcladding 11 be provided to at least partially cover the support wiremember 14 and facilitate adhesion between the support wire member 14 andthe abluminal wall surface 17 of the tubular substrate 12. In accordancewith the best mode for practicing the present invention, it ispreferable that the polymeric cladding 11 be selected from the group ofbiocompatible polymeric materials consisting of polytetrafluoroethylene,polyurethane, polyethylene, polypropylene, polyamides, polyimides,polyesters, polypropylenes, polyethylenes, polyfluoroethylenes,silicone, fluorinated polyolefins, fluorinated ethylene/propylenecopolymer, perfluoroalkoxy fluorocarbon, ethylene/tetrafluoroethylenecopolymer, and polyvinylpyrolidone.

As will hereinafter be described more fully, the polymeric cladding 11may be coupled to the support wire member 14 by any of a variety ofknown methodologies. For example, the polymeric cladding 11 may beco-extruded with the support wire member 14, the polymeric cladding 11may be extruded with an opening passing through the polymeric cladding11 along its longitudinal axis and dimensioned to receive the supportwire member 14 there through, the polymeric cladding 11 may have alongitudinally extending recess dimensioned to receive and retain thesupport wire member 14 therein, or the polymeric cladding 11 may beapplied onto the support wire member 11 in dispersion form, such as bydipcoating or spraying, and the solvent or aqueous vehicle dried therebyforming a covering on the support wire member 11.

The support wire member 14 in its polymeric cladding 11 iscircumferentially joined to the abluminal wall surface 17 of the tubularsubstrate 12, such as by helically winding at least one length ofpolymeric clad support wire member 14 in a regular or irregular helicalpattern, or by applying the polymeric clad support wire member 14 as aseries of spaced-apart circumferential rings, along at least a portionof the longitudinal axis of the abluminal wall surface 17 of the tubularsubstrate 12. It is preferable that the tubular substrate 12 be mountedonto a supporting mandrel [not shown] having an outer diameter closelytoleranced to the inner diameter of the tubular substrate 12 to permitthe tubular substrate 12 to be placed thereupon and secured theretowithout deforming the tubular substrate 12.

A second tubular member 19 may, optionally, be concentrically engagedabout the tubular member 12 and the polymeric clad support wire member14. As more clearly depicted in FIGS. 2-3, where the second tubularmember 19 is employed and disposed circumferentially about the tubularmember 12 and the polymeric clad support wire member 14, the tubularmember 12 and the second tubular member 19 encapsulate the polymericclad support wire member 14. Where the tubular member 12 and the secondtubular member 19 are both made of longitudinally expanded ePTFE, eachwill have a microporous microstructure in which the fibrils are orientedparallel to the longitudinal axis of each of the tubular member 12 andthe second tubular member 19, throughout their respective wallthicknesses. The encapsulation of the polymeric clad support wire member14 is best accomplished by providing both the tubular member 12 and thesecond tubular member 19 as unsintered or partially sintered tubes.

After wrapping the polymeric clad support wire member 14 about theabluminal surface of the tubular member 12, and circumferentiallyengaging the second tubular member 19 thereabout, it is preferable toapply a circumferential pressure to the assembly, while the assembly ison the supporting mandrel [not shown]. Circumferential pressure may beapplied to the assembly by, for example, helically wrappingtetrafluoroethylene film tape about the abluminal surface of the secondtubular member 19 along its longitudinal axis, or by securing opposingends of the assembly on the supporting mandrel, and rolling the assemblyto calendar the assembly. After the circumferential pressure is appliedto the assembly, the assembly is then introduced into either aconvention or radiant heating oven, set at a temperature above the meltpoint of the material used to fabricate the tubular member 12, thesecond tubular member 19 and/or the polymeric cladding 11, for a periodof time sufficient to bond the tubular member 12, the second tubularmember 19 and the polymeric cladding 11 into a substantially monolithic,unitary structure. Where polytetrafluoroethylene is used, it has beenfound that it is preferable to heat the assembly in a radiant heatingoven.

FIGS. 4A-4C depict the method steps for making the inventive shapememory alloy supported intraluminal graft 10. With a first step 20,tubular member 12 is concentrically engaged onto a supporting mandrel 22such that the supporting mandrel 22 resides within the lumen of thetubular member 12. A helical winding of polymeric clad support wiremember 14 is applied about the abluminal wall surface 17 of the tubularmember 12 at step 25. The helical windings have an interwinding distance27 which is preferably at least one times the distance 29 whichrepresents the width of the polymer cladding 11, in the case of a planarpolymer cladding 11, or the diameter, in the case of a tubular polymercladding 11 having a circular transverse cross-section.

The helical winding of the polymeric clad support wire member 14contacts the abluminal wall surface 17 of the tubular member 12 at aninterfacial region 28. According to one preferred embodiment of thepresent invention there is provided an adhesive material 23 selectedfrom the group consisting of polytetrafluoroethylene, polyurethane,polyethylene, polypropylene, polyamides, polyimides, polyesters,polypropylenes, polyethylenes, polyfluoroethylenes, silicone,fluorinated polyolefins, fluorinated ethylene/propylene copolymer,perfluoroalkoxy fluorocarbon, ethylene/tetrafluoroethylene copolymer,and polyvinylpyrolidone. The adhesive material is preferably applied tothe interfacial region 28 of the polymeric clad support wire member 14,but may also be applied in a pattern directly to a surface of thetubular substrate and the SMA wire member 14 brought into contact withthe adhesive material. In this manner, as the polymeric clad supportwire member 28 is helically applied to the abluminal wall surface 17 ofthe tubular member 12, the adhesive material 23 forms an interlayerintermediate the polymeric clad support wire member 28 and the abluminalwall surface 17 of the tubular member 12.

Where the selected adhesive material 23 has a melt point less than thecrystalline melt point of polytetrafluoroethylene, i.e., about 327degrees Centigrade, the resulting assembly of step 25 may be introducedinto a heating oven set at the melt temperature of the selected adhesivematerial 23, for a period of time sufficient to melt the adhesivematerial 23 and impart an adhesive bond between the polymeric cladsupport wire member 14 and the tubular member 12. On the other hand,where the selected adhesive material 23 is polytetrafluoroethylene, anexternal covering of a second tubular member 26 may be concentricallyengaged about the assembly resulting from step 25, a circumferentialpressure exerted to the second tubular member 26, thereby bringing thesecond tubular member 26, the polymer clad support wire member 11 andthe tubular member 12 into intimate contact with one another, and theentire assembly introduced into a sintering oven set at a temperatureabove the crystalline melt point of polytetrafluoroethylene and for aperiod of time sufficient to meld the second tubular member 26 and thetubular member 12 to one another to form a resultant substantiallymonolithic structure which is substantially devoid of interfacialdemarcations between the second tubular member 26 and the tubular member12, with the polymer clad support wire member 14 residing intermediatethere between.

Turning now to FIGS. 5-12, there is depicted numerous alternateconfigurations of the polymer clad support wire member 14. FIGS. 5 and 6depict a first embodiment of the polymer clad support wire member 34 inwhich the support wire member is formed as a planar ribbon wire 38having a generally tubular box-like polymer cladding 36 provided aboutthe outer surfaces of the planar ribbon wire 38. In the transversecross-sectional view of FIG. 6 it will be seen that both the planarribbon wire 38 and the polymer cladding 36 have generally quadrilateralcross-sectional configurations.

FIGS. 7-8 depict a second embodiment of the polymer clad support wiremember 40 in which the support wire member is formed as a cylindricalwire 44 having a generally tubular polymer cladding 42 provided aboutthe outer circumference of the planar ribbon wire 44. In the transversecross-sectional view of FIG. 8 it will be seen that both the cylindricalwire 44 and the polymer cladding 42 have generally circularcross-sectional configurations.

FIGS. 9-12 are provided in the transverse cross-sectional views only, itbeing understood that like FIGS. 5 and 7, each of the embodimentsdepicted in FIGS. 9-12 have corresponding perspective configurations.FIG. 9 depicts a third embodiment of the polymer clad support wiremember 46 in which the support wire member is formed as a cylindricalwire having a generally triangular-shaped polymer cladding 48, with acentral longitudinal cylindrical bore to accommodate the cylindricalwire 49 therein, which is provided about the outer surfaces of thecylindrical wire 49. A fourth embodiment of the polymer clad supportwire member 50 is depicted in FIG. 10. Polymer clad support wire member50 consists generally of a polymer cladding 52 having a plurality ofplanar surfaces and having a generally quadrilateral transversecross-sectional shape, while the support wire member 54 is generallycylindrical with a generally circular transverse cross-section.

As depicted in FIG. 11, a fifth embodiment of the polymer clad supportwire member 60 is depicted. Here, the support wire member 54 has agenerally cylindrical shape with a generally circular transversecross-section, while the polymer cladding 62 has a main body portionhaving a generally circular transverse cross-section, but has additionalprojections extending radially outward from the generally circular mainbody portion to increase the bonding surface area of the polymer cladsupport wire member 60. Finally, as depicted in FIG. 12, the sixthembodiment of the polymer clad support wire member 70 is depicted. Inaccordance with this sixth embodiment there is provided a generallycylindrical support wire member 76 having a generally circulartransverse cross-section, while the polymer cladding 72 is provided witha generally triangular cross-sectional shape, with hemispherical recess74 formed in an apex of the generally triangular cross-sectional shape.The hemispherical recess 74 subtends at least a 180 degree arc andextends along a substantial longitudinal extent of the polymer cladding72. The generally cylindrical support wire member 76 is engaged in thehemispherical recess 74 and retained therein by an interference fit, orby other suitable means, such as an adhesive.

It will be understood by those skilled in the art, that each of theforegoing embodiments of the polymer clad support wire member may bemade by pulltrusion methods in which the shape memory alloy wire member,having a pre-programmed austenite phase, is fed into an extruder duringextrusion of the polymer cladding, or by extruding the polymer claddingwith a central lumen, dimensioned appropriately to permit engagement ofthe shape memory alloy wire, then threading the support wire member intothe central lumen of the polymer cladding.

Finally, an alternative embodiment of a shape memory alloy supportedintraluminal graft 80 is depicted in FIGS. 13 and 14. The inventiveshape memory alloy supported intraluminal graft 80 may be formed byhelically wrapping a length of polymer clad 84 shape memory alloy wire86 about a supporting winding mandrel, such that the polymer cladding 84has overlapping regions 88 which form seams. The resulting assembly isthen heated above the melt point of the polymer cladding 84 to join andseal the overlapping regions 88 to one another.

The inventive method 100 for making the inventive wire supportedintraluminal graft, described above, is illustrated with reference toFIG. 15. An elastic or thermoelastic wire member is provided at step 102along with a shaping mandrel 104. The shaping mandrel 104 is preferablya solid cylindrical or tubular cylindrical stainless steel membercapable of withstanding annealing temperatures of shape memory alloys.At step 106, the wire member provided at step 102 is wound onto theshaping mandrel provided at step 104. The wire member is preferablyhelically wound about the shaping mandrel such that adjacent windingsare substantially uniformly spaced from one another. It is alsocontemplated that the wire member may be wound about the shaping mandrelin any of a wide number of configurations, including non-uniformlyspaced windings long portions of the shaping mandrel, such that certainregions of the winding have higher and lower frequency windings thanother regions, that the winding be shaped as adjacent circumferentialloops such as that shape disclosed in Gianturco, U.S. Pat. No. 4,907,336or Wiktor, U.S. Pat. No. 4,969,458, both hereby incorporated byreference as teaching a shape of winding suitable for use with thepresent invention, or virtually any other shape which is capable forforming an open tubular structural skeleton, including, withoutlimitation, a helical winding having a plurality of sinusoidal bendsalong a length thereof, as taught by Wiktor, U.S. Pat. No. 4,886,062 orPinchuck, U.S. Pat. No. 5,019,090, both hereby incorporated by referenceas teaching alternative configurations of helical windings of wiremembers.

Where a thermoelastic shape memory alloy (SMA) wire member is utilized,the SMA wire member is wound about the shaping mandrel, the shape of thewound SMA wire member is programmed at step 108 by annealing the SMAwire member at a temperature and for a time sufficient to impart shapememory properties to the SMA wire member. At step 110, the preprogrammedSMA alloy wire member is then exposed to temperature conditions belowthe Mf temperature of the SMA alloy. While it is maintained below the Mftemperature of the SMA alloy, the wire member is removed from theshaping mandrel and straightened to a linear shape at step 112. If theSMA alloy wire member is to be covered with a cladding, a polymerictubular cladding is provided at step 118 and the SMA alloy wire memberis threaded into the lumen of the tubular cladding at step 120.

It is preferable that steps 118 and 120 be performed while the SMA alloywire member is maintained at a temperature below the Mf temperature ofthe SMA alloy to prevent shape recovery of the SMA alloy wire member.Alternatively, if no polymeric cladding is to be employed, but the SMAalloy wire member from step 112 is to be adhered, an adhesive materialmay be applied to the SMA alloy wire member at step 122. Step 122 may beconducted while the SMA alloy wire member is at a temperature below theMf temperature, however, due to the fact that most adhesives may notadhere to the SMA alloy wire member at such temperatures, the adhesiveis preferably applied to the SMA alloy wire member while it is in theaustenite state. Where an elastic wire member, such as a supportstructure made from stainless steel spring wire, is employed, the shapeprogramming described in the preceding paragraph may, of course, beomitted.

After application of the polymeric cladding at steps 118 and 120, orafter the adhesive is applied at step 122, or where step 122 isconducted at a temperature below the Mf temperature of the SMA alloy,the SMA wire is then exposed to a temperature excursion to above theA_(f) temperature of the SMA alloy at step 114 so that the SMA alloywire member recovers its programmed shape at step 116. Where an elasticwire member is employed, it is not sensitive to temperature excursionsand the temperature excursion step may be omitted.

A tubular substrate, made of, for example, extruded ePTFE, preferablyextruded ePTFE which has been radially deformed from its nominalextruded diameter to an enlarged diameter, or woven polyester, isprovided at step 123. The wire member in its enlarged shape, which inthe case of an SMA wire member is its programmed shape, or in the caseof an elastic wire member, in its unstressed state, is concentricallyengaged about the tubular substrate at step 124, and joined to thetubular substrate at step 126 by thermally bonding the adhesive or thepolymeric cladding to the abluminal or luminal surface of the tubularsubstrate. It is preferable that step 126 be conducted while the tubularsubstrate is supported by a support mandrel and that the SMA alloy wiremember is retained in intimate contact with a surface of the tubularsubstrate with at least a portion of the wire member. The wire member,either in its clad or unclad state, may be retained in intimate contactagainst either by tension wrapping the wire member or by an externalcovering wrap of a release material, such as polytetrafluoroethylenetape, to cover at least a portion of the wire member.

After the wire member is joined to the tubular substrate, the assemblymay optionally be sterilized at step 128, such as by exposure toethylene oxide for a time and under appropriate conditions to sterilizethe assembly. Where an SMA alloy wire member is employed, the assemblyis then exposed to a temperature below the As temperature of the SMAalloy wire member at step 130 and the assembly is mechanically deformedto a smaller diametric profile at step 132. Where an elastic wire memberis employed, the assembly is mechanically deformed to a smallerdiametric profile at step 132 largely independent of temperatureconditions. Step 132 may be performed by any suitable means to reducethe diametric profile of the assembly, such as by drawing it through areducing die, manually manipulating the assembly to a reduced diametricprofile, or folding the device.

The reduced profile assembly is then loaded onto a delivery catheter andcovered with a restraining sheath at step 134. Once loaded onto adelivery catheter and covered with a restraining sheath to prevent shaperecovery. In the case where the wire member is an SMA alloy, loading theassembly onto a delivery catheter and covering with a restraining sheathrequires that step 134 be performed at a temperature below the A_(s)temperature of the SMA alloy wire in order to prevent thermoelasticrecovery of the SMA alloy wire member. Where, however, the wire memberis fabricated of an elastic material, the loading step 134 is notlargely temperature sensitive and may be performed at room temperature.While the wire member will exert shape recovery forces at roomtemperature, e.g., above the A_(s) temperature of the SMA alloy wireemployed, the restraining sheath of the delivery catheter will preventthe SMA alloy wire member from recovering its programmed shape andcarrying the tubular substrate to the programmed shape of the SMA alloywire member. Optionally, the sterilization step 128 may also beperformed after the assembly is loaded onto the delivery catheter atstep 134.

While the present invention has been described with reference to itspreferred embodiments and the best mode known to the inventor for makingthe inventive shape memory alloy supported intraluminal graft, it willbe appreciated that variations in material selection for the polymercladding, for the shape memory alloy, or process variations, such as themanner of winding the polymer clad support wire member about either awinding mandrel or a tubular member, or times and conditions of themanufacturing steps, including material selection, may be made withoutdeparting from the scope of the present invention which is intended tobe limited only by the appended claims.

1. A method for forming a self-expanding stent-graft, comprising:coupling a shape memory member to a polymer cladding to form a polymerclad member; winding a length of the polymer clad member about a mandrelso that adjacent windings include regions of polymer cladding thatoverlap; heating the wound polymer clad member to join and seal theoverlapping regions to one another; manipulating the stent-graft from afirst diameter to a second diameter smaller than the first diameter; andloading the stent-graft into a restraining sheath, wherein therestraining sheath prevents the stent-graft from reverting to the firstdiameter.
 2. The method according to claim 1, wherein the coupling stepcomprises completely surrounding the shape memory member with thepolymer cladding.
 3. The method according to claim 2, wherein thecoupling step comprises coextruding the shape memory wire member withthe polymer cladding.
 4. The method according to claim 2, wherein thecoupling step comprises extruding the polymer cladding with a centrallumen dimensioned to receive the shape memory wire member and threadingthe shape memory member into the central lumen.
 5. The method accordingto claim 1, wherein the coupling step comprises extruding the polymercladding with a longitudinally extending recess dimensioned to receiveand retain the shape memory member and placing the shape memory memberinto said longitudinally extending recess.
 6. The method according toclaim 1, wherein the coupling step comprises dip-coating the shapememory member, wherein the polymer cladding is in solvent or aqueousform, and drying the polymer cladding.
 7. The method according to claim1, wherein the coupling step comprises spraying the shape memory memberwith the polymer cladding in solvent or aqueous form and drying thepolymer cladding.
 8. The method according to claim 1, wherein thecoupling step comprises disposing an adhesive between the shape memorymember and the polymer cladding.
 9. The method according to claim 1,further comprising the step of bonding the polymer clad member to aninner generally tubular substrate.
 10. The method according to claim 1,further comprising the step of bonding the polymer clad member to anouter generally tubular substrate.
 11. The method according to claim 1,further comprising the step of disposing the polymer clad member betweenan inner generally tubular substrate and an outer generally tubularsubstrate.
 12. The method according to claim 11, wherein the inner andouter generally tubular substrates comprise expandedpolytetrafluoroethylene.
 13. The method according to claim 1, furthercomprising the step of selecting the polymer cladding material from thegroup consisting essentially of polytetrafluoroethylene, polyurethane,polyethylene, polypropylene, polyamide, polyimide, polyester,polyfluoroethylenes, silicone, fluorinated polyolefin, fluorinatedethylene/propylene copolymer, perfluoroalkoxy fluorocarbon,ethylene/tetrafluoroethylene copolymer, polyvinylpyrrolidone, andcombinations thereof.
 14. The method according to claim 1, wherein priorto the coupling step, the step of preparation of the shape memory membercomprises: winding the shape memory member about a shaping mandrel;imparting shape memory characteristics to the shape memory member byheating at a temperature to achieve generally an austenite phase of theshape memory material; cooling the shape memory member to a temperatureto achieve generally a martensite phase of the shape memory material;and straightening the shape memory member.
 15. The method according toclaim 1, wherein the manipulating comprises exposing the stent-graft toa temperature below the austenite temperature of the shape memory memberand deforming the stent-graft.
 16. The method according to claim 15,wherein the deforming step is selected from the group consistingessentially of manually deforming the stent-graft, drawing thestent-graft through a die, folding the stent-graft, and combinationsthereof.
 17. The method according to claim 16, further comprisingsterilizing the stent-graft.
 18. The method according to claim 1,further comprising sterilizing the stent-graft.